Add documentation for Deleted Projects page

Dan Jensenrequested to merge
djensen-add-documentation-for-admin-deleted-projects-interface into master

What does this MR do and why?

In 13.3 an admin-level page was introduced to display Deleted Projects. However, we forgot to document it. This adds a section to the admin documentation to explain this page.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

Edited by Dan Jensen

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